1. Field of the Invention
This invention relates to a semiconductor circuit, preferably one formed from a Group III-V compound and, more specifically, to improvements in dielectric and metallization parameter value determination therefor.
2. Brief Description of the Prior Art
In the fabrication of semiconductor circuits from Group III-V compounds, gold and gold alloys are the most commonly employed metals for making electrical contact to the device substrate. These contacts, as well as the first level of interconnect, are usually formed by a lift off process, wherein a dielectric, typically plasma deposited silicon nitride, is deposited onto the surface of the Group III-V semiconductor wafer. The wafer is coated with a photo-sensitive masking material and the masking material is exposed through a patterned reticle and then developed to leave an appropriate pattern on the dielectric surface. The exposed dielectric is then etched away, typically using plasma etching, then slightly undercut to ensure that metal evaporated onto the semiconductor substrate through the masking material will not be continuous over the mask pattern and dielectric side walls. A solvent for the masking material is then employed to dissolve the masking material by attacking it through the discontinuity in the evaporated metal and "lifting off" the metal that is on the dissolved masking material. Once all of the contacts are formed, the semiconductor wafer is appropriately cleaned, and a second dielectric layer is plasma or CVD deposited. In the prior art, this dielectric has typically been silicon dioxide. Silicon dioxide has poor adhesion to gold. This poor adhesion of silicon dioxide to gold often leads to a continuity failure.
Also, in the prior art, as stated hereinabove, interconnect metalization was largely provided by lift-off patterning. This technique suffered both from limitations in device complexity available to obtain reasonable yield using the technique and also from reliability problems. GaAs circuits are often required to operate in high radiation environments and a characteristic of gold based interconnect is that soft x-ray absorption can produce excessive heating of the gold. The resulting coefficient of thermal expansion-induced stresses cause the deposited interconnect and insulating dielectrics to separate.